Sexual differences in 5'-deiodinase activity in the Harderian gland of Syrian hamsters and the effect of pinealectomy: regulation by androgens

Sexual differences on thyroxin 5'-deiodinase (5'-D) in the Harderian gland of Syrian hamsters were investigated. We compared the 24-h profile of 5'-D activity in male and female hamsters, observing a clear rhythm in males but not in females. Female values were always significantly higher than male ones. After pinealectomy day/night variations in male 5'-D activity at the time points studied were abolished, results that are in correlation with serum thyroid hormones. We also studied the regulation by androgen of the enzyme activity. Basal 5'-D activity increased in castrated males and levels fell when animals were implanted with testosterone or its product 5 alpha-dihydrotestosterone (DHT). Female 5'-D activity was also inhibited by androgens. As only the addition of DHT in the presence of epitestosterone, an inhibitor of the conversion of testosterone on DHT, in castrated males was able to decrease 5'-D activity to the control animal levels, we suggest a probable direct effect of DHT by itself.

Invasive processes in the normal Harderian gland of Syrian hamster

In this contribution we will pay special attention to several morphological findings that we can observe, under some circumstances, in the normal Harderian gland of the Syrian hamster. The accumulation of porphyrins in this gland results in mitochondrial damage and extensive cell death. Many damaged cells are secreted into the lumen of the tubule-alveoli, but most of them seem to produce an invasive process that even affects the vascular components of the gland. In this way, many blood vessels are invaded and appear partially filled with the invasive mass, which sometimes totally occludes the lumen of the vessels. We have also observed other surprising features related to a special kind of activity in certain secretory cells. Such activity results in a peculiar "segregation" of a cytoplasmic fragment, containing the nucleus. The affected cells seem to gather up their cytoplasm and nucleus towards the basal zone, while the rest of the cell, including practically the whole amount of lipid droplets, is relegated to the vicinity of the lumen. All these phenomena seem finally to result in the detachment of some clusters, composed of a limited number of cells, which display a basophilic cytoplasm practically free of lipid droplets.

Regulation of the aminolevulinate synthase gene in the Syrian hamster Harderian gland: changes during development and circadian rhythm and role of some hormones

The Syrian hamster Harderian gland has been advocated as a model to study the porphyrin biosynthetic pathway, since it shows by far the highest porphyrin concentration known to date. Another particular characteristic is the sexual dimorphism at both the morphological and the biochemical levels. We found a variation in the ALV-S (aminolevulinate synthase) gene expression according to sex, with females exhibiting much higher mRNA levels than do males. After castration, ALV-S mRNA rose considerably in males, this increase being inhibited by darkness or treatment with melatonin. Treatment with hCG or progesterone did not vary the ALV-S mRNA levels in females. Castrated males, however, showed a much larger increase when they were treated with hCG. No variations have been found in the expression of the ALV-S gene in female HG throughout the estrous cycle. During development, males and females showed similar ALV-S mRNA levels until they were 20 days old. Afterwards, they started showing gender-associated differences. In females, ALV-S mRNA levels rose during the first 3 months of life, and thereafter they decreased progressively with aging. A circadian rhythm has been found in the gene expression of ALV-S mRNA in females, showing very low levels in the morning and reaching a peak during the first hours of darkness. It was an endogenous rhythm, probably regulated at the transcriptional level. It is proposed that the light-dark period duration modulates this rhythm through the suprachiasmatic nucleus which in turn acts on the pineal secretion of melatonin that regulates ALV-S gene expression.

The pineal neurohormone melatonin prevents in vivo and in vitro apoptosis in thymocytes

Recently, melatonin was found to be the most potent physiological free radical scavenger known to date. In this work, we attempted to define the role this neurohormone plays in the regulation of apoptosis, since the effect of bcl-2, the main gene implicated in its inhibition, acts via an antioxidant mechanism. We investigated the role of melatonin in cell death of thymus, a well known model for the study of apoptosis. Two sets of experiments were carried out: in vivo experiments, performed with Wistar rats, and in vitro experiments, performed with primary cultures of young Wistar rat thymocytes treated with glucocorticoids in order to induce apoptosis. Morphometrical studies in semithin sections of thymus and analysis of DNA fragmentation by gel electrophoresis show that physiological apoptosis occurring in thymus of 65 days old rats, is prevented by the daily administration of melatonin beginning when the rats were 25 days old. Also, we found that at a concentration of 10(-7) M, melatonin decreases by 35% the percentage of apoptotic cells induced by glucocorticoids in cultured thymocytes of 25 day old rats. 10(-9) M melatonin decreases cell death by 20%. Finally, melatonin at 10(-11) M did not have any effect. Several hypothesis are discussed to explain this effect: direct interaction of melatonin with glucocorticoid receptors in the thymus; induction of interleukin-4 release; direct genomic action modulating the expression of apoptosis-inhibiting genes; an effect on nitric oxide synthase; and finally, the antioxidant action of melatonin. Since apoptosis is a possible mechanism involved in neuronal death shown in several neurodegenerative diseases such as Parkinson or Alzheimer's diseases, investigative efforts should be directed to the possible role of melatonin in inhibiting cell death in tissues other that the thymus. Melatonin might be a potent therapeutic agent in some of these conditions.

Melatonin stimulates the activity of the detoxifying enzyme glutathione peroxidase in several tissues of chicks

The pineal hormone melatonin has been shown to directly scavenge free radicals and to stimulate, in the mammalian brain, at least one enzyme, glutathione peroxidase, which reduces free radical generation. In the present studies, we examined the effect of melatonin on glutathione peroxidase activity in several tissues of an avian species. Melatonin (500 micrograms/kg), when injected into chicks, increased glutathione peroxidase activity within 90 min in every tissue examined. Tissue melatonin levels, measured by radioimmunoassay, also increased following its peripheral administration. Depending on the tissue, the measured increases in melatonin varied from 75% to 1,300% over the control values. The melatonin-induced increases in glutathione peroxidase activity varied with the tissue and were between 22% and 134%. These percentage increases in glutathione peroxidase activity were directly correlated with tissue melatonin content. These results suggest that melatonin induces the activity of the detoxifying enzyme, glutathione peroxidase, in several tissues in the chick. The findings also suggest that melatonin would reduce the generation of highly toxic hydroxyl radicals by metabolizing its precursor, hydrogen peroxide. Because of this ability to stimulate glutathione peroxidase activity, melatonin should be considered as a component of the antioxidative defense system in this avian species.

Red-light-induced suppression of melatonin synthesis is mediated by N-methyl-D-aspartate receptor activation in retinally normal and retinally degenerate rats

Pineal gland N-acetyltransferase (NAT) activity and pineal and serum levels of melatonin declined linearly in albino rats acutely exposed to different intensities of red light (600 nm or higher; low, 140 microW/cm2; moderate, 690 microW/cm2; high, 1200 microW/cm2) during the middle of the night. The high intensity red light was as effective as white light (780 microW/cm2) in suppressing NAT activity and pineal and circulating melatonin. Red-light-inhibited nighttime NAT activity and suppressed nocturnal melatonin levels in both retinally degenerate and normal rats. Pretreatment with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (10 mg/kg intraperitoneally) completely prevented the red-light-induced inhibition of nighttime melatonin synthesis. Magnesium chloride (300 mg/kg intraperitoneally) reduced the inhibitory effects of low and moderate intensities of red light but was ineffective when high red-light intensity was used. However, both agents failed to antagonize the suppression of nighttime melatonin synthesis elicted by the exposure to white light. Since retinally degenerate and retinally normal animals respond in the same way to both red-light and pharmacological intervention with the NMDA receptor blocker MK-801, the findings indicate that the activation of central hypothalamic NMDA receptors might mediate the photic inhibition of nocturnal melatonin synthesis in the pineal gland elicited by the exposure to red light at night. Red-light-induced suppression of nocturnal melatonin synthesis possibly can be used to investigate the biochemical mechanisms by which light entrains melatonin synthesis and to study the pharmacological and physiological effects of endogenous and synthetic agents that antagonize the NMDA receptor response.

Melatonin stimulates brain glutathione peroxidase activity

Exogenously administered melatonin causes a 2-fold rise in glutathione peroxidase activity within 30 min in the brain of the rat. Furthermore, brain glutathione peroxidase activity is higher at night than during the day and is correlated with high night-time tissue melatonin levels. Glutathione peroxidase is thought to be the principal enzyme eliminating peroxides in the brain. This antioxidative enzyme reduces the formation of hydroxyl radicals formed via iron-catalyzed Fenton-type reactions from hydrogen peroxide by reducing this oxidant to water. Since the hydroxyl radical is the most noxious oxygen radical known, induction of brain glutathione peroxidase might be an important mechanism by which melatonin exerts its potent neuroprotective effects.

Circadian rhythms in reproductive and thyroid hormones in gonadally regressed male hamsters exposed to natural autumn photoperiod and temperature conditions

Two groups of young adult male Syrian hamsters were kept in a vivarium at 22 degrees C and a light:dark cycle of 14.5:9.5 h (lights on 06.30 h; indoor) or in a naturally decreasing photoperiod and fluctuating ambient temperature conditions (outdoor) from October 1 (day length 11 h 50 min) to November 30 (day length 10 h 12 min). Representative animals from each group were killed at 3-hour intervals with additional time points near the onset of light. Weights of the paired gonads and accessory organs revealed that all of the animals kept outdoors and none of those kept indoors underwent reproductive regression. Significant circadian rhythms were observed in serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), thyrotropin (TSH), thyroxine (T4), triiodothyronine (T3) and testosterone in indoor and outdoor-housed hamsters. The 24-hour acrophase in serum LH, TSH, T4 and T3 occurred between 13.00 and 16.00 h, while that of serum testosterone and PRL occurred between 18.00 and 20.00 h in indoor hamsters. Hormonal variables in which there was a significant alteration in the 24-hour acrophase of outdoor animals relative to that in the indoor animals included pituitary PRL and serum testosterone, PRL, FSH and TSH. Hamsters housed indoors had a significant rhythm in brown adipose tissue type-II 5'-deiodinase activity, but no rhythm was evident in this tissue in outdoor animals. The natural autumnal conditions depressed serum LH and testosterone around the clock, though the depression of serum FSH relative to indoor hamster values was best seen between 09.00 and 21.00 h and that for PRL between 15.00 and 24.00 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor-1 in Syrian hamsters: interactions of photoperiod, gonadal steroids, pinealectomy, and continuous melatonin treatment

Four experiments in Syrian hamsters examined the role and possible interaction of photoperiod, gonadal steroids, and the pineal on circulating levels of insulin-like growth factor-1 (IGF-1). In the first experiment, female hamsters were exposed to long photoperiod (LP; 14:10 LD) or short photoperiod (SP; 8:16 LD); an additional group of SP-exposed females was pinealectomized (PX). SP induced a significant depression in IGF-1 concentrations which PX partially prevented. In Experiment 2, two groups (control and castrate [CX]) of adult male hamsters were kept in LP, and three groups (intact, CX, and CX+PX) of hamsters were kept in SP for five weeks. The four groups of animals that were CX and/or maintained in SP had approximately the same mean level of IGF-1, and all four groups were significantly (P < 0.001) higher than the LP-control hamsters. In Experiment 3, four groups (intact controls, CX, CX+melatonin pellet [MEL PEL], and MEL PEL only) were kept in LP. Melatonin pellets (1 mg melatonin/24 mg beeswax/every two weeks) were implanted sc twice during the experiment. Castration induced a rise (P < 0.001) in IGF-1 levels, and this was not prevented by MEL PEL. In Experiment 4, testosterone and dihydrotestosterone pellets implanted in LP-exposed CX males prevented the CX-induced rise in IGF-1; testosterone implants also reduced IGF-1 levels in CX males treated with progesterone. In conclusion, SP treatment depresses IGF-1 in female hamsters and raises it in males. These results substantiate previous studies in other models of gonadal steroid deficient animals. They lend further credence to the hypothesis that there is a sexual dimorphism in circulating IGF-1 concentrations in the Syrian hamster that may be at least partially related to the presence of gonadal steroids.

Melatonin binding sites in the harderian gland of the rat and Syrian hamster

Specific melatonin binding sites in the harderian gland of both rat and Syrian hamster were studied using [125I]melatonin. In both species, binding of [125I]melatonin by harderian gland membranes exhibited properties such as dependence on time, temperature, membrane concentration, saturability, and high specificity. Only one class of high-affinity binding sites was found with a Kd of 0.19 and 6.47 nM for the rat and Syrian hamster, respectively. The binding capacity in the rat harderian gland was 4.00 fmol/mg protein; in the Syrian hamster it was 7.58 fmol/mg protein. In the rat, no sex differences were found in the binding of the tracer to the membranes. However, in the Syrian hamster, binding of [125I]melatonin by the harderian gland was twice higher in the female than in the male. No changes were found in the Kd values (6.47 vs. 6.94 nM), while binding capacity was significantly increased in the female (13.50 fmol/mg protein) when compared to the male hamster (7.58 fmol/mg protein). Binding of [125I]melatonin by the harderian gland of male hamsters was modified by castration but not by melatonin treatment. Castration induced an increase of binding up to the level of females. However, chronic melatonin administration did not alter the [125I]melatonin binding in either intact or gonadectomized male hamsters. Binding studies also showed diurnal variations. There was a diurnal rhythm of [125I]melatonin binding by Syrian hamster harderian glands with the peak at the end of the light period and the trough late in the dark period. This rhythm in the binding is observed in both male and female hamsters, although binding in females was always higher than that in males.(ABSTRACT TRUNCATED AT 250 WORDS)

Pineal acid phosphatase activity in Syrian hamsters: sex differences and effects of castration and androgen replacement therapy

Pineal acid phosphatase (ACP) activity was examined in seven experiments involving young intact or castrated male and female Syrian hamsters. Nine-week old female hamsters had a 3-fold (p < 0.001) higher ACP activity in their pineal glands than did males. After three weeks of castration, a significant increase (p < 0.001) in ACP activity occurred in castrated male pineal glands. In males, pellets with 5 alpha-dihydrotestosterone (p < 0.01) but not testosterone or progesterone suppressed pineal ACP activity. In females, no changes in pineal ACP activity were noted due to the estrous cycle. Pineal ACP activity was not affected by testosterone, dihydrotestosterone or androstenedione pellets in intact females or by testosterone pellets in ovariectomized animals.

Nuclear localization of melatonin in different mammalian tissues: immunocytochemical and radioimmunoassay evidence

Melatonin was detected by an improved immunocytochemical technique in the cell nuclei of most tissues studied including several brain areas, pineal gland, Harderian gland, gut, liver, kidney, and spleen from rodents and primates. Cryostat sections from tissues fixed in Bouin's fluid, formalin, or acetone/ethanol were used. The nuclear staining appeared primarily associated with the chromatin. The nucleoli did not exhibit a positive reaction. The melatonin antiserum was used in the range of 1:500 to 1:5,000. Incubation of the antibody with an excess of melatonin resulted in the complete blockade of nuclear staining. Pretreatment of the sections with proteinase K (200-1,000 ng/ml) prevented the positive immunoreaction. In a second aspect of the study, we estimated the concentration of melatonin by means of radioimmunoassay in the nuclear fraction of several tissues including cerebral cortex, liver, and gut. The subcutaneous injection of melatonin (500 micrograms/kg) to rats resulted, after 30 min, in a rapid increase in the nuclear concentration of immunoreactive melatonin which varied in a tissue-dependent manner. However, samples collected 3 h after the injection showed that melatonin levels had decreased to control values. Pinealectomy in rats resulted in a clear reduction in the nuclear content of melatonin in the cerebral cortex and liver but not in the gut. The results of these studies suggest that melatonin may interact with nuclear proteins and that the indole may have an important function at the nuclear level in a variety of mammalian tissues.

Melatonin receptors in purified cell nuclei of liver

Specific binding of [125I]iodomelatonin to homogenates from purified rat liver nuclei was characterized. The binding is rapid, reversible, saturable and of high affinity. Specific binding seems to be found in the nuclear protein fraction, since after precipitation of the proteins with trichloroacetic acid, the specific binding disappeared. The Kd (180 +/- 20 pM) and Bmax (9.1 +/- 0.03 fmol/mg protein) values (mean +/- S.E.M.) agree with the melatonin concentration in nuclei and may imply a physiological locus for melatonin action.

Mast cells in the Harderian gland of female Syrian hamsters during the estrous cycle and pregnancy: effects of the light/dark cycle

The number of identifiable mast cells and the intraluminal area occupied by porphyrin deposits was studied on semithin sections from female hamster Harderian glands during the estrous cycle and pregnancy. Although the serum levels of estradiol, progesterone, luteinizing hormone and follicle stimulating hormone exhibited significant changes throughout the cycle, no correlation between these changes and the variations in the number of recognizable mast cells was observed. However both during diestrous 1 and proestrous cycles, the number of identifiable mast cells was higher at midnight than at noon (in 14 h light:10 h dark photoperiod with lights on at 07:00 h). A more exhaustive study revealed the presence of 'degranulated mast cells' which were not stained with toluidine blue. Thus, a diurnal cycle in degranulation might occur in the Harderian glands from female hamsters. No significant variations were observed in the area occupied by intraluminal porphyrin deposits during the estrous cycle. However, both the relative number of mast cells and the area occupied by intraluminal porphyrins decreased from day 4 of pregnancy to day 14 showing a strong correlation. The Harderian glands from female Syrian hamsters might provide a useful model for the study of mast cell degranulation during porphyria.

Distribution of melatonin in mammalian tissues: the relative importance of nuclear versus cytosolic localization

Besides its presence in the pineal gland, melatonin has been found in a variety of other tissues as well. The indoleamine also has been identified in invertebrates including an unicellular organism where it exhibits a diurnal rhythm. Although melatonin is mainly known for its effects on seasonal reproduction and endocrine physiology, there is evidence showing that this ubiquitously acting hormone is also a potent free radical scavenger, thereby providing protection from oxidative attack to DNA and other biomolecules. Through the years, melatonin was thought to be exclusively cytosolic. However, careful examination of some of these pioneering reports revealed a nuclear localization of melatonin in different tissues including the retina and Harderian glands. Using a very sensitive immunocytochemical method, we have also found that melatonin is located in the nucleus of many cells where it may bind to nuclear components. The use of cell fractionation studies followed by radioimmunoassay confirmed these results. The administration of exogenous melatonin resulted in a marked increase in the nuclear melatonin content without a concomitant change in the cytosolic fraction. In addition to its ability to scavenge free radicals, its location in the nucleus suggests possible genomic actions.

Gender-associated differences in the development of 5-aminolevulinate synthase gene expression in the harderian gland of Syrian hamsters

The mRNA levels for aminolevulinate synthase (ALV-S), the rate-limiting enzyme in porphyrin synthesis, were studied in male and female Syrian hamsters during postnatal development. Sex-associated differences in the expression of ALV-S gene were evident at the end of the third week of postnatal development. Serum levels of luteinizing hormone (LH), testosterone, cortisol, thyroid hormones and insulin-like growth factor were also studied in order to correlate their concentrations with the mRNA levels for ALV-S. Among these hormones, serum LH levels showed a positive correlation with the ALV-S mRNA levels. However, the expected negative correlation with testosterone levels was not clearly observed. Thus, in order to test the effects of testosterone on ALV-S gene expression, 11-day-old male and female Syrian hamsters and adult female hamsters were injected with 50 micrograms of testosterone for 4 days. Testosterone administration decreased the levels of ALV-S mRNA in the adult females but did not influence those of young females. The possible explanation for the insensitivity to testosterone during these postnatal stages might involve the maturational state of androgen receptors in the Harderian glands.

Thyroxine 5'-deiodinase type II activity in chick pineal and Harderian gland: nyctohemeral rhythmicity and its regulation by noradrenergic input

Circadian rhythmicity of type II thyroxine 5'-deiodinase (5'-D) activity was studied in the pineal gland and Harderian glands of chicks. Only Harderian 5'-D activity showed a nyctohemeral rhythmicity with a maximal peak during the day time (1300), while no rhythm of enzyme activity was found in the pineal gland. Besides type II 5'-D activity, we found high basal levels of the type I isoenzyme in both glands; this activity was specifically suppressed by the addition of 6-n-propyl-thiouracil (PTU). However, day-night differences in Harderian 5'-D activity were maintained even after the addition of PTU. This activity was not affected for either continuous light exposure or darkness during the day. 5'-D activity seems to be regulated by the noradrenergic input, since the enzymatic activity was stimulated by a beta-adrenergic agonist, isoproterenol, and by the alpha-adrenergic agonist, phenylephrine, in both pineal and Harderian glands. Both drugs affected 5'-D activity in the Harderian gland by stimulating the enzyme activity over basal levels.

Melatonin binding sites in the Harderian gland of Syrian hamsters: sexual differences and effect of castration

The presence of specific melatonin binding sites in the Harderian gland of Syrian hamsters was studied using [125I]melatonin. Saturation binding experiments conducted with [125I]melatonin at 37 degrees C using Harderian glands of both male and female Syrian hamsters revealed a single nanomolar-affinity site. The dissociation constants (Kd) were 6.47 and 6.94 nM for males and females, respectively. The concentration of the binding sites was 7.58 fmol/mg protein for males and 13.50 fmol/mg protein for females. Castration of male hamsters resulted in a significant increase in [125I]melatonin binding sites while chronic melatonin administration did not modify the binding properties. The results confirm the presence of melatonin binding sites in the Harderian glands of rodents. The gender-associated differences found together with the effects of castration in male hamsters suggest an androgenic control in [125I]melatonin binding sites of the Syrian hamster Harderian gland.

Chronic N-methyl-D-aspartate administration prevents melatonin-associated changes in cell differentiation in the harderian glands of male hamsters

The daily administration of 25 micrograms of melatonin for 10 weeks resulted in an increase in the percentage of Type II cells in the Harderian glands of male Syrian hamsters. Harderian glands of melatonin injected animals consisted of 65-70% Type II cells while control animals which were injected with saline had 40% Type II secretory cells. The daily administration of 3 mg of the glutamate receptor agonist N-methyl-D-aspartate (NMDA) prevented the effects of melatonin on cell differentiation but was without effect when administered to saline treated hamsters alone. Both the relative number of mitoses and the number of total cells, estimated by counting the nuclei, was not affected. Thus, a conversion from Type I to Type II cells seems possible. The effects of melatonin and NMDA administration were independent of the serum levels of testosterone, luteinizing hormone and thyroxine, hormones which have been implicated in Type II cell differentiation. However, prolactin levels, which were affected by melatonin and NMDA administration, might be involved in the differentiation of Harderian gland secretory cells.

Testosterone sensitive dihydropyridine binding in the Harderian gland of the male hamster

It is well known that in different tissues, dihydropyridines bind at nanomolar concentrations to a receptor and block voltage-operated Ca2+ channels. In studies reported here, Harderian gland tissue homogenates from intact male hamsters exhibited significant dihydropyridine binding (Bmax = 1700 fmoles/mg protein) of high affinity (Kd = 1.1 nM). Tissue homogenates from female animals exhibited a similar Kd value (1.35 nM) but receptor density per mg protein was significantly reduced (Bmax = 270 fmoles). Dihydropyridine binding of Harderian gland tissue homogenates from castrated males was reduced greater than 80% (Bmax = 225 fmoles/mg protein). Treatment of castrated males with subcutaneous testosterone pellets resulted in significant restoration of dihydropyridine binding activity (approximately 80%, Bmax = 1630 fmoles/mg protein) with a comparable binding constant (Kd = 1.50 nM) as observed for noncastrated, control animals. Addition of testosterone (ex vivo) to homogenates from castrated hamsters did not restore dihydropyridine binding to control levels. These data indicate: (a) the Harderian gland from male hamsters exhibits significant dihydropyridine binding; (b) ligand binding is abolished following castration; and (c) significant restoration of dihydropyridine binding occurs following in vivo testosterone treatment. The dependence of dihydropyridine binding restoration upon in vivo steroid hormone administration suggests probable involvement of the steroid at the transcriptional level although non-genomic mechanisms such as the binding of testosterone to a receptor resident in the plasma membrane and subsequent activation of Ca2+ channels can not be ruled out.

Effects of human chorionic gonadotropin and progesterone administration on porphyrin biosynthesis and histology of the Harderian glands in male and female Syrian hamsters

We investigated the influence of hCG and progesterone on the control of porphyrin biosynthesis and histology in the Syrian hamster Harderian glands. Castration of male hamsters caused a marked elevation in porphyrin biosynthesis as revealed by the concentrations of porphyrins and the mRNA levels of the porphyrin pathway rate-limiting enzyme, 5-aminolevulinate synthase (ALV-S). Injection of hCG into castrated male hamsters also resulted in a significant increase in both porphyrin concentrations and levels of ALV-S mRNA compared with those in saline-injected castrated hamsters. Type II cells, which are filled with large lipid vacuoles and are characteristic of male phenotype, disappeared after castration, but administration of hCG partially prevented this change. On the other hand, neither administration of hCG nor progesterone implants could increase the very high porphyrin concentrations and ALV-S mRNA levels characteristic of female Syrian hamsters. As in the case of castrated male hamsters, injections of 20 IU hCG to female Syrian hamsters increased the relative number of Type II cells per square millimeter, whereas progesterone administration did not modify the relative number of Type II cells. These results indicate that hCG can modify Harderian gland morphology in both male and female hamsters and can exert a positive control in the expression of ALV-S gene in castrated male hamsters.

Development and hormonal regulation of mast cells in the Harderian gland of Syrian hamsters

The morphological features and relative number of mast cells per mm2 were studied in the Harderian glands of male and female Syrian hamsters (Mesocricetus auratus) under different experimental conditions. The structural and ultrastructural characteristics of Harderian mast cells corresponded to those of connective tissue mast cells. The Harderian glands from female hamsters contained more mast cells than those of male hamsters. A subcutaneous implant of testosterone (2 mg/24 mg beeswax) resulted in a rapid decrease in the number of recognizable mast cells 6 h after the implantation. Neither orchidectomy nor ovariectomy significantly altered the relative number of mast cells. However, the daily subcutaneous injection of 20 IU of human chorionic gonadotropin during 20 days resulted in a significant decrease of identifiable mast cells. The administration of another steroid such as progesterone or the induction of states of hypo- and hyperthyroidism did not alter the distribution of mast cells in the Harderian glands of female Syrian hamsters.

Porphyrin metabolism in the harderian glands of Syrian hamsters: in vivo regulation by testicular hormones, lighting conditions, pineal gland, and pituitary hormones

The porphyrin concentration in the harderian glands of male hamsters subjected to several endocrine manipulations was studied. Prolonged bilateral gonadectomy resulted in a marked increase in harderian porphyrin concentration. This change was not prevented by either pinealectomy or by constant white light exposure. Castrated hamsters exposed to constant red light showed higher porphyrin concentrations than castrated hamsters kept under white light. Among several hormones studied, serum luteinizing hormone and thyroid-stimulating hormone levels were unexpectedly higher in the constant red light exposed group than in the other groups. In order to test whether luteinizing hormone was involved in the postcastrational rise in harderian porphyrins, we administered a potent luteinizing hormone-releasing hormone (LHRH) agonist. The chronic administration of the LHRH agonist resulted in a decrease in serum luteinizing hormone (because it desensitized the LHRH receptors on the gonadotropes) and, consequently, in serum testosterone levels. However, no rise in harderian porphyrin was observed. It is concluded that the absence of testicular hormones might not be the triggering factor involved in harderian porphyrogenesis.

Female Syrian hamster Harderian gland: development and effects of high environmental temperature and melatonin injections on histology and porphyrin deposits

We have investigated the development of the Harderian glands of female Syrian hamsters from birth to 8 months of age. The effects of melatonin injections on Harderian gland histology and porphyrin deposits of female hamsters exposed to two different temperatures were also studied. The morphology of the Harderian glands from 30-day-old female hamsters resembled those of sexually mature adult animals. The intraluminal area occupied by porphyrins increased significantly between 20 to 30 days of age. However, the relative number of mast cells per mm2 rose between 30 to 90 days. Both porphyrins and mast cell numbers appeared clearly reduced in the 8-month-old group. Secretory cells characterized by large lipid droplets (type II cells) were not observed. Daily afternoon injections of 25 micrograms of melatonin to female hamsters exposed to 22 degrees C for 14 weeks resulted in the discontinuity of estrous cyclicity, a marked decrease in the intraluminal area occupied by porphyrins, a reduction of the number of mast cells per mm2, and in a marked augmentation of the number of type II cells per mm2. Although the administration of similar dosages of melatonin to hamsters exposed to an environmental temperature of 32 degrees C did not interrupt estrous cycles, a clear reduction of the area occupied by porphyrins was observed. However, the number of mast cells and type II cells per mm2 was unaffected in these animals. Our results suggest that hormones other than ovarian steroids are involved in the regulation of the female hamster Harderian glands. The possible role of melatonin on Harderian gland metabolism is discussed.

Age and food restriction alter the porphyrin concentration and mRNA levels for 5-aminolevulinate synthase in rat Harderian gland

The effects of age and food restriction on the porphyrin concentration in Harderian glands were studied in male Fisher 344 rats. Harderian gland porphyrin concentrations increased with age; this was statistically significant in 20 month old animals compared with 3 month old animals. Food restriction (by 40%) prevented the age-associated rise in porphyrins; thus, in 20 month old food restricted rats had porphyrin concentrations similar to those found in young animals. In a second experiment, we correlated the age-associated rise in Harderian gland porphyrin concentrations with an increase in mRNA levels for 5-aminolevulinate synthase (ALV-S). Both the porphyrin concentration and ALV-S mRNA rose at 12 and 18 months of age, but decreased by 24 months of age. It is concluded that, a) porphyrin biosynthesis in the Harderian glands increases up to 20 months of age but decreases in rats that are 24 months old, and b) food restriction prevents the porphyrin rise associated with age in the Harderian gland of male Fisher 344 rats.

Serum luteinizing hormone, prolactin, and thyrotropin and their pituitary subunit mRNA levels during proestrus in the Syrian hamster

mRNA levels for alpha, luteinizing hormone beta (LH beta), and prolactin (Prl) were examined during the hamster estrous cycle, with sampling most frequent (1-hour intervals) on the afternoon of proestrus. These transcripts encode the peptide subunits for the pituitary hormones LH and Prl which are necessary for reproductive function. Serum hormone levels of LH and Prl, analyzed by 24-hour periodic regression, exhibited a 24-hour periodicity on proestrus characterized by a large surge peaking at about 18.00 h. Combining the data for non-proestrous days of the cycle disclosed a rhythm with similar timing for LH and Prl. Thyroid-stimulating hormone (TSH) and TSH beta RNA profiles during hamster proestrus are reported for the first time. Serum TSH exhibited a pronounced peak coincident with that of the other hormones on proestrus. Because of variations at other times on the day of proestrus, however, a 24-hour periodicity was not manifested by regressional analysis. Combined non-proestrous serum TSH data also revealed no consistently timed regressional 24-hour periodicity. During proestrus, pituitary mRNA values for alpha, LH beta, and Prl simultaneously exhibited a rise from the lowest to the highest of all proestrous values in the 3-5 h prior to the time of the pre-ovulatory peak of circulating hormone concentrations. RNA for TSH beta exhibited an earlier, broader peak on proestrus. Periodic regression indicated a significant 24-hour rhythm for alpha mRNA in data pooled from non-proestrous days (acrophase 05.00 h) and for TSH beta mRNA on proestrus (acrophase 04.54 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Gender differences and time course of castration-induced changes in porphyrins, indoles, and proteins in the Harderian glands of the Syrian hamster

Sexual differences and the effects of orchidectomy were determined for porphyrin and melatonin concentrations and for the activities of the enzymes N-acetyltransferase and hydroxyindole-O-methyltransferase, which synthesize melatonin from serotonin, in the Harderian glands of the Syrian hamster. Porphyrin concentrations in intact males were about 1/400th those of intact females. Castration for 1 week increased male Harderian porphyrin concentrations 10-fold; by 3 weeks, castrated male porphyrin levels were 140 times those of control values. N-Acetyltransferase activity in intact male Harderian glands was about 4 times that of females. Castration led to a drop in N-acetyltransferase activity to female levels within 2 weeks. Hydroxyindole-O-methyltransferase activity was 7 times higher in females than in males and castration had no effect on male Harderian hydroxyindole-O-methyltransferase activity. Neither gender nor castration influenced Harderian melatonin concentrations. Soluble proteins in Harderian glands from male and female hamsters and from male hamsters castrated for 1 and 4 weeks were examined by sodium dodecyl sulfate--polyacrylamide gel electrophoresis. The gel profiles revealed several differences among the protein distribution in male and female gland lysates. Orchidectomy led to a female protein pattern within 4 weeks.

Inhibition of 5 alpha-reductase does not simulate the effects of androgen deprivation on porphyrin metabolism by harderian glands from the male Syrian hamster

As 5 alpha-reductase is involved in the metabolism of indolamines in the Harderian glands of Syrian hamsters, we have compared the effects of androgen deprivation and the administration of the potent 5 alpha-reductase inhibitor N,N-diethyl-4-methoxy-3-oxo-4-aza-5-androstene-17-carboxamida on Harderian porphyrin metabolism. Ten days after castration, porphyrin levels had increased to 40 times the values of intact hamsters. However, the inhibition of 5 alpha-reductase, which resulted in a significant decrease in the weight of accessory sex glands, did not modify porphyrin concentrations within the Harderian glands. It is concluded that, contrary to the situation for indolamine metabolism, testosterone per se is the main androgen involved in the sexual differences observed in Harderian porphyrin metabolism.

5-aminolevulinate synthase mRNA levels in the Harderian gland of Syrian hamsters: correlation with porphyrin concentrations and regulation by androgens and melatonin

The levels of 5-aminolevulinate synthase mRNA were investigated in the Harderian glands of male and female Syrian hamsters by using a cDNA clone from rat liver. Female hamsters showed higher levels of mRNA than those in males, while the administration of testosterone to female hamsters led to a reduction in mRNA levels. Castration of male hamsters caused a marked elevation of mRNA levels, whereas both the exposure to constant darkness or melatonin injections to castrated males partially prevented the effects of castration. Porphyrin concentration of Harderian glands showed a strong correlation with the mRNA levels of 5-aminolevulinate synthase in all the animals studied. These results lead to the conclusion that in this system, porphyrin metabolism is controlled through hormonal regulation of 5-aminolevulinate synthase gene expression.

Chronic administration of melatonin induces changes in porphyrins and in the histology of male and female hamster harderian gland: interrelation with the gonadal status

In this paper, we have investigated the influence of melatonin on the histology and porphyrin content of the Syrian hamster Harderian glands. Daily afternoon injections of 25 micrograms of melatonin to female hamsters for 12 weeks resulted in the discontinuity of estrous cyclicity, a marked decrease in the Harderian gland intraluminal area occupied by porphyrins, and in a significant rise in the number of Type II cells. A similar decrease in porphyrins was observed after 8 weeks of ovariectomy. However, if the melatonin injections were given for only 8 weeks (without inducing gonadal atrophy), no changes were observed in the area occupied by intraluminal porphyrins, suggesting that the effects of melatonin in female Syrian hamsters might be associated with the subsequent gonadal atrophy. Castration of male hamsters induced a significant increase in porphyrins and a clear drop in the number of Type II cells. These changes were totally prevented when melatonin was administered daily from the day of castration. Our results suggest that melatonin, at least in male Syrian hamsters, plays a role in Harderian metabolism, acting directly on the Harderian secretory cells or indirectly through pituitary hormones.

Harderian gland porphyrin, lysosomal and type II 5'-deiodinase rhythms in Sprague-Dawley and Fischer-344 rats kept under chronic long- or short-photoperiod conditions

1. Harderian gland porphyrin concentrations were 1.5-fold higher in Fischer-344 male rats than in Sprague-Dawley male rats and there were no differences due to exposure to LD 14:10 (LP) or LD 10:14 (SP) lighting conditions for 8 weeks in either strain. 2. 24-hr periodic regression analyses of porphyrin concentration detected a significant rhythm in both lighting conditions in both strains, with no differences in acrophase due to lighting conditions. 3. In both strains, porphyrin levels were highest in the late phase-early dark period and fell during the early part of the dark period. 4. Acid phosphatase activity did not vary with time (circadian rhythm), strain or photoperiodic lighting condition. 5. Circadian rhythms in beta-glucuronidase, alpha-mannosidase and hexosaminidase activity were present in some instances, but, probably due to the low amplitude to these rhythms, a consistent effect of strain or housing condition was not found. When 24-hr rhythms were observed in either strain, the acrophase occurred during the afternoon-early evening daylight period. 6. A significant effect of strain on mean values of type II 5'-deiodinase activity was noted in Fischer-344 rats. 7. Significant rhythms in type II 5'-deiodinase activity were found in both strains exposed to LD 10:14.

Indole and porphyrin content of the Syrian hamster harderian glands during the proestrous and estrous phases of the estrous cycle

Porphyrin and indole metabolism was studied in the Harderian glands of Syrian hamsters during the proestrous and estrous stages of the estrous cycle. Porphyrins remained unaltered during these stages, but levels of different indoles (5-hydroxytryptophan, 5-hydroxytryptamine, N-acetyl-5-hydroxytryptamine, and 5-hydroxyindole acetic acid) exhibited pronounced changes during the dark:light period in both proestrous and estrous. There was a strong parallelism between 5-hydroxytryptamine, N-acetyl-5-hydroxytryptamine and 5-hydroxyindole acetic acid levels. Hydroxytryptophan rhythms appeared slightly shifted from those of the other indoles. Immunoreactive melatonin present in the Harderian glands did not show a significant day-night change during the stages studied.

N-acetyltransferase activity in the Harderian glands of the Syrian hamster, Mesocricetus auratus, is regulated by androgens and by hormones of the pituitary-thyroid axis

This study tested the hypothesis that activity of the enzyme N-acetyltransferase (NAT) in the Harderian gland of the Syrian hamster is regulated both by androgens and by hormones of the pituitary-thyroid axis. To test the effects of castration and hypothyroidism, intact or castrated male hamsters were given either tap water or methimazole in their drinking water for 3 weeks. Methimazole suppresses iodination of thyroglobulin, thereby decreasing circulating levels of thyroid hormones and increasing TSH levels. Hypothyroidism or castration caused elevated or depressed Harderian gland NAT activities respectively, compared with euthyroid controls. When castration and hypothyroidism were combined, the animals exhibited high NAT activity compared with castrated euthyroid males. To test the effects of castration and hyperthyroidism, male hamsters were given daily injections of thyroxine (T4) or diluent and were either castrated or left intact for 4 weeks. Intact animals given T4 had depressed Harderian NAT activity; serum thyroid hormone levels were elevated and TSH levels were depressed compared with those of intact controls. Castrated animals had depressed NAT activity below that of intact controls; serum thyroid hormone levels were normal but TSH levels were depressed. Castrated animals given T4 injections had NAT activity similar to that of euthyroid castrated hamsters; thyroid hormone levels were elevated but TSH levels were similar to those seen in euthyroid castrated hamsters. In another experiment, both T4 and tri-iodothyronine (T3) were equally effective in decreasing NAT activity in intact males. To determine the effects of the removal of pituitary influences, male hamsters were hypophysectomized. NAT activity in the Harderian glands of these animals was reduced compared with intact controls.(ABSTRACT TRUNCATED AT 250 WORDS)

mRNA transcription determines the lag period for the induction of pineal melatonin synthesis in the Syrian hamster pineal gland

The nocturnal pattern of Syrian hamster pineal melatonin synthesis is characterized by a 6-8 h lag period, followed by a late-night, short-duration peak in both N-acetyltransferase (NAT) activity and melatonin content. Administration of cycloheximide (20 mg/kg body weight) given either at the time of lights out or 4 h into the dark phase to Syrian hamsters blocked the nocturnal increase in both pineal NAT activity and melatonin content. Actinomycin D (5 mg/kg body weight) prevented the nocturnal increase in both constituents only when it was administered at darkness onset, being significantly less effective when injected after 4 h of dark exposure. Reinduction of melatonin production by isoproterenol (2 mg/kg body weight) administration to acutely light-exposed animals during late darkness was prevented by cycloheximide, but not by actinomycin D administration. The results suggest that whereas Syrian hamster pineal melatonin production requires protein synthesis both early and late in the dark phase, the transcription of a putative NAT-related mRNA, which occurs only during the early night, seems to determine the lag period in melatonin synthesis and pineal responsiveness to beta-adrenergic receptor agonist stimulation.

Ultrastructural study of the cellular types in the pineal organ of Gambusia affinis (teleost)

The pineal organ of Gambusia affinis was studied via light and electron microscopy. The cell types studied included photoreceptor cells, supporting cells, and a third cell type. The photoreceptor cells, which appear to form clusters, are divided into four regions: outer segment, inner segment, cell soma, and synaptic pedicle. Synaptic ribbons are commonly observed in the synaptic pedicle. The supporting cells separate the photoreceptor cells from the thick basal lamina that surrounds the entire pineal organ. The supporting cells show highly organized membrane formations, some lipid-like inclusions, and a diplosome. One of the centrioles gives rise to an invaginated cilium. The third cell type is observed infrequently and appears to be located mainly in the vicinity of the outer segments. The morphological characteristics of this cell type are similar to those of phagocytic cells. The ultrastructural features of the pineal organ of G. affinis are compared with those of other teleosts.

Ultrastructure of the blood vessels in the Harderian gland of the hamster (Mesocricetus auratus): existence of sinusoids

The Harderian gland blood supply of female and male hamsters was studied using light and electron microscopy. A profuse vascularization surrounding secretory acini was observed. Among the blood vessels, the existence of large and irregular sinusoidal capillaries was apparent. These sinusoids appeared in close association to the basal aspect of the secretory cells. Typical, small, fenestrated capillaries were also observed within the connective tissue. The existence of this particular vascularization together with other morphological features of the secretory cell basal pole suggest a possible endocrine function of these orbital glands.

Treatment with forskolin for 8 hours during the day increases melatonin synthesis in the Syrian hamster pineal gland in organ culture: the long lag period is required for RNA synthesis

The exposure of organ-cultured pineal glands of Syrian hamsters to forskolin, an adenylate cyclase activator, caused marked increases in melatonin levels when glands were collected in the second half of the dark period and incubated for 4 h. However, when glands were collected at the beginning of the dark period and incubated with the same drug, a significant increase in melatonin content was observed only after 6-8 h. Likewise, when glands were collected at the beginning of the light period, forskolin stimulated melatonin synthesis only after 6-8 h of incubation with the drug. These results support the existence of a relatively long lag period necessary for the induction of melatonin production in the Syrian hamster pineal gland. Experiments with actinomycin D indicate that RNA synthesis occurs during the lag period; thus, actinomycin D blocks the induction of melatonin synthesis by forskolin in glands collected at the beginning of the dark period and incubated for 8 h. In contrast, when pineal glands were collected from hamsters killed in the second half of the dark period, and incubated with forskolin for either 4 or 8 h, actinomycin D was unable to block the induction of melatonin production. These data suggest that RNA, presumably messenger RNA, which is necessary for increasing hamster pineal melatonin synthesis, is synthesized and accumulates during the first half of the night.

In vivo administration of isoproterenol or forskolin during the light phase induces increases in the melatonin content of the Syrian hamster pineal gland without a rise in N-acetyltransferase activity

In vivo melatonin production was stimulated during the daytime in pineal glands of female Syrian hamsters following the administration of several injections of either isoproterenol, a beta-receptor agonist, or forskolin, an adenylate cyclase stimulator. The large increase in melatonin following either isoproterenol or forskolin administration was not accompanied by significant changes in N-acetyltransferase (NAT) activity. The results suggest that the Syrian hamster pineal gland, as in other species, responds by producing melatonin during the light phase if the stimulus is adjusted to its particular and specific regulatory mechanisms, i.e., if beta-adrenergic stimulation is continued for 4-8 h. The lack of a commensurate increase in NAT activity raises the question of the need of maximal enzymatic activity for a significant rise in melatonin production in the Syrian hamster pineal gland.

Androgenic control of N-acetyltransferase activity in the harderian glands of the Syrian hamster is mediated by 5 alpha-dihydrotestosterone

N-acetyltransferase (NAT) activity in the Harderian glands of intact and gonadectomized male and female Syrian hamsters was evaluated. The exogenous administration of 5 alpha-dihydrotestosterone (DHT) to castrated males and intact females produced an increase in NAT values, which reached the values present in the glands of intact males. The administration of a 5 alpha-reductase inhibitor to intact males led to a decrease in NAT activity, suggesting that testosterone is converted in DHT within the glands. It is concluded that NAT activity in the Syrian hamster Harderian glands is under androgenic control, the active steroid being DHT.

Effects of short-day photoperiods and of N-(2,4-dinitrophenyl)-5-methoxytryptamine, a putative melatonin antagonist, on melatonin synthesis in the Harderian gland of the Syrian hamster, Mesocricetus auratus

The Harderian glands of Syrian hamsters contain melatonin and the enzymes N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) which synthesize melatonin from serotonin. Because the Harderian glands share this metabolic pathway with the pineal gland, we examined the effects of short-day photoperiods, which stimulate pineal-mediated gonadal regression, and N-(2,4-dinitrophenyl)-5-methoxytryptamine (ML-23), which has been described as a melatonin antagonist, on melatonin synthesis in the Harderian glands of the hamster. Harderian glands of male hamsters kept in short days had reduced NAT activity and melatonin concentration, but HIOMT activity was unchanged from that of long-day controls. In males kept in short days, ML-23 restored melatonin concentrations to levels seen in long days but did not affect the short-day induced reduction in NAT activity. ML-23 had no effect upon NAT or HIOMT activity or melatonin concentration in male hamsters kept on long days. Harderian glands of female hamsters kept on short days had reduced melatonin concentrations, but NAT and HIOMT activities similar to those of long-day controls. ML-23 had no effect on Harderian NAT or HIOMT activities or melatonin concentration in females kept in short days. However, in females kept in long days, ML-23 treatment led to increased NAT activity and decreased melatonin concentrations. We conclude from these results that short-day photoperiods alter some aspects of melatonin synthesis in hamster Harderian glands and that these effects differ in males and females. ML-23 does not usually prevent the effects of short days on Harderian melatonin synthesis, suggesting that it is not a melatonin antagonist in the Syrian hamster.

Melatonin and porphyrin in the harderian glands of the Syrian hamster: circadian patterns and response to autumnal conditions

1. Adult male Syrian hamsters were killed at nine intervals during a 24 hr period in the autumn, after 2 months either indoors in controlled conditions or in natural outdoor conditions. 2. Harderian glands were taken for determination of N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) activities and melatonin and porphyrin concentrations. 3. Mean 24 hr Harderian NAT and melatonin values were lower outside than inside. 4. Twenty-four hour melatonin rhythms were detected with similar daytime (afternoon) acrophases in both environmental conditions. 5. An NAT rhythm was seen only in animals kept inside, with a circadian maximum in the late dark phase. 6. Mean 24 hr HIOMT activity was slightly higher outdoors than indoors, and 24 hr rhythms were not detected in either condition. 7. Mean porphyrin concentrations were higher outdoors, with 24 hr rhythms detected in both conditions and a significantly earlier nocturnal circadian maximum outdoors.

5 alpha-dihydrotestosterone administration converts indolamine metabolism and porphyrin content of the female Syrian hamster Harderian gland to the male type

The effects of ovariectomy and exogenous androgen administration on the indole and porphyrin metabolism of Syrian hamster Harderian glands were studied. Ovariectomy alone had no effect on any of the parameters analyzed. The administration of either testosterone or 5 alpha-dihydrotestosterone increased the activity of N-acetyltransferase in the Harderian glands. However, androgen treatment failed to change the activity of hydroxyindole-O-methyltransferase. Melatonin content of the glands dropped 20 days after treatment with testosterone and 10 days after the administration of 5 alpha-dihydrotestosterone. The porphyrin content of the Harderian glands was dramatically depressed after the administration of either androgen. It is concluded that the Harderian glands of Syrian hamsters are under an androgenic control involving 5 alpha-dihydrotestosterone.

Testosterone increases N-acetyltransferase activity in both male and female Syrian hamster harderian glands

N-acetyltransferase (NAT) activity was studied in the Harderian glands of intact and castrated (with or without subcutaneous testosterone implants) male and female Syrian hamsters. Castration in male hamsters produced a significant drop in the NAT activity. Castrated males with testosterone implants had NAT activity levels comparable to those in intact males. Ovariectomy did not modify NAT activity. Ovariectomized hamsters with testosterone implants exhibited a significant increase in the Harderian NAT activity reaching the same values as those in the glands of the male hamsters.

Histochemical detection of monoamine oxidase and alcohol dehydrogenase activities in the Syrian hamster Harderian glands: existence of a sexual dimorphism

Monoamine oxidase (MAO) and alcohol dehydrogenase (AD) activities were studied histochemically in the Syrian hamster Harderian gland using tryptamine as substrate and Nitroblue Tetrazolium as the final electron acceptor. No dark: light-related changes were observed. Male type I secretory cells showed an intense MAO reaction. Female type I cells exhibited a moderate MAO activity. Both male and female glands showed a moderate/intense AD-positive reaction. Male type II cells were lacking MAO and AD activities. MAO activity found in the hamster Harderian glands corresponded mainly to MAO type A since treatment with chlorgyline (0.01, 0.1 and 0.5 mM) totally inhibited it. The possible role of these two enzymes in Harderian gland indolalkylamine metabolism is discussed.

Bromocriptine prevents the castration-induced rise in porphyrin concentration in the harderian glands of the male Syrian hamster, Mesocricetus auratus

The Harderian glands in Syrian hamsters exhibit a striking sexual dimorphism. Male Harderian glands show two cell types and low levels of porphyrins and melatonin. Of the enzymes involved in the synthesis of melatonin, N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) show high and low activity levels, respectively. Female Harderian glands show but one cell type and have high porphyrin and melatonin levels, low NAT activity, and high HIOMT activity. In castrated males, the Harderian glands exhibit a female pattern of morphology, porphyrin levels, and indoleamine metabolism. In an attempt to determine whether prolactin in involved in this sexually dimorphic response of the Harderian glands, intact and castrated male and intact female hamsters were injected daily with 500 micrograms of bromocriptine, a dopamine agonist. Bromocriptine led to reduced serum prolactin levels in all groups. It had no apparent effect on the Harderian glands of intact males. In contrast, in castrated males bromocriptine prevented the postcastrational rise in porphyrin levels but had no effect on NAT or HIOMT activities. In females, bromocriptine treatment had no effect on porphyrin concentrations or HIOMT activity; it led to a statistically significant increase in NAT activity. We propose that testosterone inhibits Harderian porphyrin synthesis while dopamine or prolactin stimulates it.

Role of postsynaptic alpha-adrenergic receptors in the beta-adrenergic stimulation of melatonin production in the Syrian hamster pineal gland in organ culture

The role played by postsynaptic alpha-adrenergic receptors in the stimulation of pineal melatonin production was investigated in the Syrian hamster. The studies were conducted using organ cultured pineal glands collected from both anatomically intact and superior cervical ganglionectomized hamsters. Results obtained indicate that phenylephrine, an alpha-adrenergic agonist, by itself has no effect in promoting melatonin production; however, it potentiates the stimulatory effects of isoproterenol, a beta-adrenergic agonist, on pineal melatonin production in nonoperated hamsters. Similar observations were obtained with pineal glands whose presynaptic terminals were removed by prior superior cervical ganglionectomy. However, a longer incubation time was required (4-6 hours vs. 2 hours) with pineal glands taken from ganglionectomized animals. Apparently, beta-adrenergic activation is an absolute requirement to stimulate pineal melatonin production, and an alpha-adrenergic receptor mechanism potentiates beta-adrenergic activation. In addition, the findings obtained with denervated pineal glands suggest that the regulation of pineal melatonin production by both alpha- and beta-adrenergic mechanisms is through receptors located on postsynaptic structures.

N-acetyltransferase activity and indole contents of the male Syrian hamster Harderian gland: changes during the light:dark cycle

The activities of N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) and the indole contents of the Harderian glands of male Syrian hamsters were studied throughout a 24-h period. NAT activity exhibited a sharp rise 1 h after lights on, decreasing to basal levels 1 h later. Neither a HIOMT activity nor a melatonin concentration rhythm was detected throughout the 24 h. The 5-hydroxytryptamine (serotonin) concentration was highest during the dark phase reaching a peak at 0300 h; with light onset serotonin levels exhibited a rapid short-term drop. The 5-hydroxytryptophol concentration was highest during the mid- to late photophase; the lowest values to this constituent were measured late in the dark phase and at 1 h after lights on. The 5-hydroxyindole acetic acid concentration of the Harderian glands was rather stable throughout the 24-h period but levels did show a short-lived drop 1 h after light onset. Only a few animals contained detectable amounts of N-acetyl-5-hydroxytryptamine (N-acetylserotonin) in their Harderian glands. In agreement with previous work on the Harderian glands of female Syrian hamsters, the present results in males suggest that light onset is associated with marked changes in Harderian indoleamine metabolism.

Beta-adrenergic stimulation prior to darkness advances the nocturnal increase of Syrian hamster pineal melatonin synthesis

Pineal glands of male Syrian hamsters stimulated in vivo with isoproterenol (ISO) for 4 h before the onset of darkness showed a 4-h advance in the timing of the nighttime increases in both N-acetyltransferase activity and melatonin levels. When ISO (1 mg/kg) was administered every 2 h to animals kept in light during the night, a significant increase in melatonin synthesis was observed after 4-6 h. The results suggest that the Syrian hamster pineal gland can respond in vivo to continuous beta-adrenergic stimulation, but a lag period of 4-6 h is required before there is an increase in melatonin synthesis.

Differential responses of rat pineal thyroxine type II 5'-deiodinase and N-acetyltransferase activities to either light exposure, isoproterenol, phenylephrine, or propranolol

1. Compared to pineal N-acetyl transferase (NAT) activity, which exhibited a dramatic drop following acute light exposure at night, nocturnal rat pineal thyroxine type II 5'-deiodinase (5'-D) activity was minimally influenced by the same light exposure. The injection of cycloheximide, a potent inhibitor of protein synthesis, although it did curtail the rise in NAT activity for at least 2 hr, did not elicit decreases in the activities of either 5'-D or NAT enzymes. Propranolol, a beta-adrenergic blocker, either delayed the continued nocturnal rise in 5'-D activity when injected at 0000 hr or slightly enhanced the fall in 5'-D activity when injected at 0200 hr. These results suggest that interruption of the synthesis of proteins is responsible for the slow deterioration of 5'-D activity induced by either light or propranolol. 2. The slight fall in 5'-D activity induced by light at night was prevented by isoproterenol; phenylephrine, however, did not prevent the fall and the effect of isoproterenol + phenylephrine was similar to that obtained with isoproterenol alone. On the other hand, the light-inhibited NAT activity recovered after the injection of isoproterenol; phenylephrine did not elicit any effect, but the injection of both isoproterenol and phenylephrine simultaneously caused a greater NAT response than that induced by isoproterenol alone. 3. When injected during the day, phenylephrine had no effect on either pineal 5'-D or NAT activities; however, the injection of either isoproterenol alone or isoproterenol + phenylephrine elicited 5-fold and 10-fold increases in nocturnal, light-suppressed 5'-D and NAT activities, respectively. During the day, phenylephrine did not potentiate the effects of isoproterenol on NAT activity as it did at night. When the effects of isoproterenol on the 5'-D activity were compared to rats exposed to light during the day and at night, the activity of 5'-D reached a higher level at night than during the day.